1. The Field of the Invention
This invention relates to valves for use in sidepocket mandrels in underground wells and, more particularly, to novel equalizing blank valve apparatus and methods for equalizing a pressure differential between the tubing and the casing of a well.
2. The Background Art
Underground wells are typically constructed so as to include a large pipe called the "casing" which extends into the earth the entire length of the well. The casing helps ensure the mechanical integrity of the well so as, for example, to keep oil and gas from contaminating adjacent water supplies. Perforations are provided through the casing at the levels of various zones in the earth containing oil or gas. Packers are also provided within the casing to isolate these zones from the upper portion of the well and also to isolate adjacent zones from each other.
A typical well structure also comprises a smaller pipe called the "tubing." The tubing is installed within the casing so as to pass through the packers and also extend the entire length of the well. In oil or gas producing wells, it is typically the tubing which conveys the oil or gas to the wellhead. Similarly, the tubing is commonly used to convey injection material into injection wells.
In order to permit communication between the tubing and the casing, sidepocket mandrels are installed as part of the tubing string. Each mandrel typically has a port which communicates with the casing, and an adjacent sidepocket is provided for installing a valve mechanism. Such valves thus allow for controlled communication between the tubing and the casing annulus surrounding the tubing at the various zone levels at which the sidepocket mandrels are installed. Thus, for example, a sidepocket mandrel may be provided with an orifice injection valve for the injection of water, corrosion inhibitors or other materials into the various zones of injection wells. Similarly, gas lift valves may be installed in the sidepocket mandrels in producing wells so as to carry out conventional gas lift methods.
A wireline running tool is usually employed to install a valve in a sidepocket mandrel. The running tool attached to the wireline is used to lower the valve into a sidepocket mandrel, and a latch mechanism is provided on the valve to lock the valve into place in the mandrel.
When it is subsequently desired to remove a valve from a sidepocket mandrel, a wireline is again run into the well to the level of the valve. A pulling tool attached to the end of the wireline is then used to secure the end of the valve latch. An upward jarring on the wireline then shears a pin in the latch mechanism, thereby releasing the valve from the sidepocket mandrel and allowing it to be removed by the wireline from the well.
Quite frequently, it is desireable that there be no communication between a particular mandrel and the surrounding casing annulus. Such is, for example, often the case in a mandrel which is located at the bottom of a deep well. It is also sometimes desireable to preclude such communication at various selected zones along the length of the well.
To prevent any communication between a mandrel and the surrounding casing annulus, a "blank" or "dummy" valve is typically employed. Dummy valves are basically a solid metal plug which has substantially the same size and configuration as a valve. The dummy valve is also provided with a latch mechanism to latch it into the sidepocket mandrel in the manner described above.
It will be readily appreciated that there is often a very large pressure differential between the tubing and the surrounding casing annulus. This pressure differential may, for example, sometimes be as great as 2,000 pounds per square inch or more. Significantly, such large pressure differentials may make it difficult, if not impossible, to subsequently remove a dummy valve which has been installed in a sidepocket mandrel in a well.
To facilitate the removal of dummy valves in cases of anticipated large pressure differentials, equalizing dummy valves have been developed. Such valves allow the pressure between the tubing and casing to be equalized before the valve is pulled, thereby making valve retrieval much easier.
Prior art equalizing dummy valves typically include a special latch mechanism. This latch includes a separate prong or "fishing head" at the top which may be pulled so as to equalize pressure between the tubing and casing. Once this prong is pulled, a tool may then be lowered by a wireline so that the valve may be released from the sidepocket mandrel and pulled from the well.
Although prior art equalizing dummy valves afford significant advantages over the use of a solid metal plug, significant disadvantages remain. For example, the need for a special latch for equalizing dummy valves significantly increases the cost and confusion at a well site due to the need to stock and use different valve latches for different situations. Moreover, special tools are typically required both to install and to retrieve prior art equalizing dummy valves. This likewise increases the cost associated with installing and maintaining such valves.
In addition, in order to retrieve a prior art equalizing dummy valve from a sidepocket mandrel, two separate wireline runs are typically required. A first run lowers the special tool which is designed to pull the equalizing fishing head on the latch mechanism of the equalizing dummy valve. A second wireline run is then required to lower the tool needed to unlatch the equalizing dummy valve from the sidepocket mandrel and raise the valve to the earth's surface. It will be readily appreciated that the necessity of making two separate wireline runs to retrieve a single valve may be a significant disadvantage, particularly in view of the fact that such valves may be located several thousand feet below the earth's surface.